Peyton Manning is the latest sports star struggling to produce a happy ending to his brilliant career.

It’s possible the 39-year-old Broncos quarterback, who entered this season with a chance to become the NFL’s all-time winningest quarterback, will not throw another pass again as a pro.

Manning, who is tied with Brett Favre with 186 regular-season wins as a starter, most likely will end the season on that number because he’ll be backup Brock Osweiler’s backup in Sunday’s regular-season finale against the Chargers.

Whether Manning, who has been out since Nov. 15 with a torn plantar fascia in his left foot, gets the chance to break Favre’s record in 2016 is in question, with the specter that this might be it for him hanging heavily in the thin Mile High air.

Something of even more weight also is hanging over Manning right now: the Al Jazeera report last weekend that suggested he obtained HGH through his wife from an Indianapolis anti-aging clinic, where he received post-operative treatment in 2011.

Manning quickly lashed out at the report, angrily denying the accusations made by a former pharmaceutical intern who has since recanted his story. The NFL is investigating the allegations — which Manning said he welcomes to “get it over with.”

“The report wasn’t true Sunday, it’s not true today and it won’t ever be true … and I’m still angry about it,’’ said Manning, who said he still is considering legal action.

“It’s kind of a shame the other stuff that’s going on with him,” Broncos tight end Owen Daniels told ESPN last week. “The guy’s done it right his whole career. We know he’s toward the end of his career now, and you hate to see people try to do stuff to legends like that. I believe in Peyton, 100 percent. I feel for him that he’s got to go through this, but if anyone can handle it, Peyton can.”

Whether or not Manning is publicly exonerated regarding the HGH allegations will go a long way toward how he’s remembered at the end of his career — whether he gets the Roger Clemens treatment or not.

Certainly, what has taken place on the field this year, in terms of his personal stats, has not left a very nice endgame impression. Manning is the last-ranked quarterback in the league and, despite having missed the past five games, still leads the NFL with 17 INTs.

Sunday’s game offers this fascinating nugget: Manning has not entered a game as a backup since his 1994 freshman season at the University of Tennessee, when he sat behind Jerry Colquitt and Todd Helton on the depth chart.

Osweiler is 4-2 as the starter, including Monday’s win over Cincinnati, which clinched a playoff berth. That leaves the chances of Manning getting to play in the postseason rather cloudy.

In a change of course from the previous two weeks, when Broncos coach Gary Kubiak waited until midweek to reveal his starting quarterback, this week he announced Monday that Osweiler would start and Manning would back up. Kubiak, too, complimented the way Manning handled the decision.

“I like the way he has battled to get to this point,’’ Kubiak said. “He’s a competitor. Everyone wants to play. But he also understands where we are at, and he wants to do what’s best for the team, and I am proud of him for that.’’